Laser self mixing interferometry plays an increasingly important role in the field of high precision measurement.Micro displacement measurement has been used in large civil structures,aerospace,health monitoring and so on.The traditional measurement is based on the amplitude modulation signal,but with the enhancement of noise,the measurement error is bigger and bigger,and even difficult to measure.For this reason,the amplitude modulation/frequency modulation (AM) signal conversion is realized by using the Mach–Zehnder interferometer.In this paper,the phase unwinding of frequency modulation signal in high noise environment is carried out by using multiple Hilbert transform,and the original signal is reconstructed.Numerical simulation results demonstrate the effectiveness of the proposed method.The SNR of the system is 10.0614 dB and the estimated error is 0.0614 dB in a 10 dB white noise environment.The experimental results show that the error of micro displacement reconstruction is within 100 nm,and the SNR of FM signal is much higher than that of AM signal.This method is suitable for ultra precision measurement and has a high signal to noise ratio in high noise environment.